Problem: Solve for $k$ : $23 + k = 18$
Explanation: Subtract $23$ from both sides: $ \begin{eqnarray} \\ 23 + k &=& 18 \\ \\ {-23} && {-23} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{23 + k} &\hphantom{=}& \hphantom{18} \\ k &=& 18 {- 23} \\ \end{eqnarray} $ Simplify. $ k = -5$